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Introduce o3tl::unsafe_downcast for known-good dynamic_cast downcasts

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(This helps rewrite code that silences Coverity unchecked dynamic_cast warnings,
like 57b89ea1c2 "coverity#704563 Unchecked dynamic
cast", in a way that is cleaner and potentially executes faster.)

Change-Id: I3319c0eeec2aa822f686feacd499a76c8c9b9499
Reviewed-on: https://gerrit.libreoffice.org/80458
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
This commit is contained in:
Stephan Bergmann 2019-10-08 14:55:25 +02:00
parent 7dbebef754
commit 8ec3116162
5 changed files with 86 additions and 6 deletions
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8
chart2/source/controller/main/DrawCommandDispatch.cxx
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@ -24,6 +24,7 @@
#include <chartview/DrawModelWrapper.hxx>
#include <com/sun/star/frame/CommandGroup.hpp>
#include <o3tl/unsafe_downcast.hxx>
#include <vcl/svapp.hxx>
#include <svl/itempool.hxx>
#include <editeng/adjustitem.hxx>
@ -161,12 +162,7 @@ void DrawCommandDispatch::setAttributes( SdrObject* pObj )
pObj->SetMergedItem( SdrTextHorzAdjustItem( SDRTEXTHORZADJUST_BLOCK ) );
pObj->SetMergedItem( makeSdrTextAutoGrowHeightItem( false ) );
SdrObjCustomShape* pShape(dynamic_cast< SdrObjCustomShape* >( pObj ));
assert(pShape);
if(pShape)
{
pShape->MergeDefaultAttributes( &m_aCustomShapeType );
}
o3tl::unsafe_downcast< SdrObjCustomShape* >( pObj )->MergeDefaultAttributes( &m_aCustomShapeType );
}
}
}

35
include/o3tl/unsafe_downcast.hxx Normal file
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@ -0,0 +1,35 @@
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
* This file is part of the LibreOffice project.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
#ifndef INCLUDED_O3TL_UNSAFE_DOWNCAST_HXX
#define INCLUDED_O3TL_UNSAFE_DOWNCAST_HXX
#include <cassert>
#include <type_traits>
namespace o3tl
{
// Do a downcast from polymorphic `BasePtr` to `DerivedPtr` when it is known that `p` is actually
// pointing to an object of derived type (or is a nullptr). This is potentially cheaper than
// dynamic_cast and helps to avoid Coverity warnings about unchecked dynamic_cast.
template <typename DerivedPtr, typename BasePtr>
std::enable_if_t<
(std::is_pointer_v<
DerivedPtr> && std::is_pointer_v<BasePtr> && std::is_base_of_v<std::remove_pointer_t<BasePtr>, std::remove_pointer_t<DerivedPtr>>),
DerivedPtr>
unsafe_downcast(BasePtr p)
{
assert(p == nullptr || dynamic_cast<DerivedPtr>(p) != nullptr);
return static_cast<DerivedPtr>(p);
}
}
#endif
/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */

16
o3tl/CompilerTest_o3tl_unsafe_downcast.mk Normal file
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@ -0,0 +1,16 @@
# -*- Mode: makefile-gmake; tab-width: 4; indent-tabs-mode: t; fill-column: 100 -*-
#
# This file is part of the LibreOffice project.
#
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.
#
$(eval $(call gb_CompilerTest_CompilerTest,o3tl_unsafe_downcast))
$(eval $(call gb_CompilerTest_add_exception_objects,o3tl_unsafe_downcast, \
o3tl/qa/compile-unsafe_downcast \
))
# vim: set noet sw=4 ts=4:

1
o3tl/Module_o3tl.mk
View file

@ -24,6 +24,7 @@ $(eval $(call gb_Module_add_targets,o3tl,\
$(eval $(call gb_Module_add_check_targets,o3tl,\
CppunitTest_o3tl_tests \
$(if $(COM_IS_CLANG),CompilerTest_o3tl_temporary) \
$(if $(COM_IS_CLANG),CompilerTest_o3tl_unsafe_downcast) \
))
# vim: set noet sw=4:

32
o3tl/qa/compile-unsafe_downcast.cxx Normal file
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@ -0,0 +1,32 @@
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
* This file is part of the LibreOffice project.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
#include <sal/config.h>
#include <o3tl/unsafe_downcast.hxx> // expected-note@o3tl/unsafe_downcast.hxx:* 0+ {{}}
struct Base
{
virtual ~Base();
};
struct Derived : Base
{
};
void f(Base* b, Derived* d)
{
o3tl::unsafe_downcast<Derived*>(b);
o3tl::unsafe_downcast<Derived const*>(b);
o3tl::unsafe_downcast<Derived&>(*b); // expected-error {{}}
o3tl::unsafe_downcast<Derived*>(d);
o3tl::unsafe_downcast<Base*>(d); // expected-error {{}}
}
/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */